There is described a vertical receiver antenna device for the electromagnetic surveying of electrically resistive targets potentially containing hydrocarbons, the receiver antenna being arranged in an antenna housing formed of a non-magnetic material, the antenna housing being arranged to be placed vertically in subsea uncompacted material and extending from a seabed downwards in the subsea uncompacted material. There is also described a method of installing a vertical receiver antenna in subsea uncompacted material.
When mapping subsea structures, for example in connection with the recovery of oil and gas, it is known to use electromagnetic mapping by measuring resistivity with a vertical field component, as it is disclosed in WO 2007/053025 A1, for example. In such mapping it is of vital importance that the orientation of a signal receiver is known, and in order to maintain high quality in the mapping data acquired, large resources are used to place the receiver dipole correctly and provide data for the relative position of the receiver dipole. It is particularly desirable to achieve accurate vertical positioning of the receiver.
WO2005/006022 A1 discloses devices and methods of mapping subsea structures by means of electromagnetically based (CSEM) resistivity measurements (CSEM), in which an EM receiver antenna is placed in the seabed and extends downwards in an underground structure. The receiver is placed in the seabed to improve and ensure the position, orientation, data quality and depth of surveying. A plurality of sensors are placed in a borehole.